I have trouble calling Indy 1-3 a trilogy, since they are three separate stories. There is no through line. Yeah they feature the same character so they meet the broader definition of a trilogy, but not in the same way as BTTF or LOTR.Indeed!
Good trilogies I rank high are
Lord of the Rings
Back to the Future
Star Wars OT
Pirates of the Caribbean 1 to 3
Star Trek II to IV
Indiana Jones 1 to 3
Dark Knight